1. Field of the Invention
This invention relates to the field of Radio Frequency Identification (RFID) tags and labels, and in particular to a method of producing such tags and devices without antenna patterning.
2. Description of the Related Art
Radio frequency identification (RFID) tags and labels (collectively referred to herein as “devices”) are widely used to associate an object with an identification code. RFID devices generally have a combination of antennas and analog and/or digital electronics, which may include for example communications electronics, data memory, and control logic. For example, RFID tags are used in conjunction with security-locks in cars, for access control to buildings, and for tracking inventory and parcels. Some examples of RFID tags and labels appear in U.S. Pat. Nos. 6,107,920, 6,206,292, and 6,262,292, all of which are hereby incorporated by reference in their entireties.
As noted above, RFID devices are generally categorized as labels or tags. RFID labels are RFID devices that are adhesively or otherwise attached directly to objects. RFID tags, in contrast, are secured to objects by other means, for example by use of a plastic fastener, string or other fastening means.
Typically, RFID devices are produced by patterning, etching or printing a conductor on a dielectric layer and coupling the conductor to a chip. These structures furthermore should be able to flex when supported at one or more ends. It is important therefore to avoid materials and constructions that add undue thickness or stiffness to the RFID tag. Considering the requirements of thinness and flexibility, conductors such as wirebonds and metal lead frame are unsuitable, as are related materials such as epoxy encapsulation, and thinner conductors are desirable (such as printed conductive inks).
RFID devices on the other hand should have adequate electrical connections, mechanical support, and appropriate positioning of the components (chips, chip connectors, antennas). Structures for these purposes can add complexity, thickness and inflexibility to the RFID device. For example, layers in addition to the dielectric substrate/connectors are sometimes added to position the radio frequency circuit and antenna in three dimensions to provide electrical bonds between the various conductors. The antenna and connecting conductors often require more than one plane of electrical wiring, i.e. the designs may use cross-overs and stacking of components.
One type of structure that may carry chips and chip connectors for incorporation in RFID devices is a “strap” or “interposer”, as disclosed for example in U.S. Pat. No. 6,606,247 or in European Patent Publication 1 039 543, both of which are incorporated by reference herein in their entireties.
Another consideration is efficiency of manufacture of RFID devices. When using thin deposited or etched conductors, the precision and definition of the printed elements of lines and spaces may be important to the performance of the tabs and the overall RFID device. Conventional patterning, etching and printing methods may not provide adequate resolution, line/space separation or other qualities necessary to deliver engineered performance. In addition, methods of manufacturing RFID devices that include combining a web of RFID chips or straps with a web of formed or printed RFID antennas are complicated by the need to account for any differences in the pitch of each web, or spacing between adjacent element on each web, so that the RFID chips or straps and antennas are aligned. Further details regarding indexing of RFID strap webs may be found in co-owned U.S. Patent Application 2003/0136503 A1, which is herein incorporated by reference in its entirety. It is also desirable from a manufacturing perspective to reduce complexity and manufacturing steps in RFID device designs, and to make efficient use of component materials (reduce waste).
Moreover, while RFID tags and labels are inexpensive, and costs of RFID devices have been going down, the size and cost of such devices may make them impractical for use with small or inexpensive items. Therefore it is important to achieve the properties described above, especially for thin flexible RFID tags and labels, through cost-effective manufacture of such devices.
From the foregoing it will be seen there is room for improvement of RFID devices and manufacturing processes relating thereto.